Potentially dangerous 92L steadily developing; Igor nears hurricane strength

By: Dr. Jeff Masters , 3:04 PM GMT on September 11, 2010

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A tropical disturbance (92L) over the Eastern Caribbean, a few hundred miles south of Puerto Rico, is steadily organizing and appears likely to develop into a tropical depression by tonight or Sunday morning. Satellite loops show an impressive and expanding region of heavy thunderstorms, with good spiral banding and respectable upper-level outflow on all sides. Long range radar out of Puerto Rico shows that heavy rains are now affecting that island, but there is no rotation to the radar echoes evident. However, the rain bands are becoming more intense and more organized. San Juan, Puerto Rico reported a heavy rain squall at 8:44 am this morning, and radar estimates suggest two inches of rain fell in this squall just southeast of San Juan. Wind shear over 92L is low, 5 - 10 knots. The waters beneath are at near-record warmth, 30°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies to the north and west of 92L, and this dry air could interfere with development at times over the next few days.


Figure 1. Morning satellite image of 92L.

Track forecast for 92L
The disturbance is moving west-northwest at 11 mph, and steering currents favor a continuation of this motion for the next three days. Model support for development is scattered. The GFS and NOGAPS models do not develop 92L. The GFDL and ECMWF models predict development, with a track taking 92L into Mexico's Yucatan Peninsula on Wednesday. The HWRF model has a more northwesterly track, taking 92L over the Dominican Republic, Haiti, and Cuba, but this model has been trending too far north in its tracks. I expect 92L will follow a path south of the islands, bringing it near or just south of Jamaica on Monday, then into the Yucatan Peninsula on Wednesday. On this track, the southern Dominican Republic can expect heavy rains of 3 - 6 inches tonight through Monday morning; southern Haiti can expect similar rains Sunday through Monday, and Jamaica and the Cayman Islands can expect heavier rains of 4 - 8 inches Monday and Tuesday. Eastern Cuba will probably escape 92L's heaviest rains in this scenario (Figure 2.)

Intensity forecast for 92L
I can't find any reason to doubt this will be a tropical storm by Sunday or Monday, and potentially a Category 1 or 2 hurricane by Wednesday, if 92L avoids passage over Hispaniola and Cuba. The SHIPS model predicts wind shear will remain low, 5 - 10 knots, through the period, and makes 92L a Category 1 hurricane by Monday night. Water temperatures are certainly warm enough to support development. The main detriment to intensification is likely to be dry air, and 92L could wrap in some of the dry air to its northwest at times, slowing down development. The first Air Force Hurricane Hunter mission into 92L is scheduled for Sunday afternoon, but there will be a research mission by the National Center for Atmospheric Research G-V jet today that will give us valuable information on 92L's large scale environment and potential for development.


Figure 2. Forecast rain amounts from 92L from the 2am EDT Saturday run of the GFDL model. This model predicts most of 92L's heaviest rains will miss Haiti, but will affect Jamaica, the Cayman Islands, and the Yucatan Peninsula. Image credit: Morris Bender, NOAA/GFDL.

Igor
Tropical Storm Igor is very close to hurricane strength, and appears destined to become a large and powerful major hurricane over the Central Atlantic in the days to come. Wind shear is moderate, 15 - 20 knots, waters are warm, 28°C, and Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. Igor will track west under the influence of a strong ridge of high pressure for the next three days, then turn more to the west-northwest in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic on Tuesday and Wednesday. This should allow Igor to pass several hundred miles to the northeast of the Lesser Antilles. In the longer range, Igor may be a threat to Bermuda, and has a slight chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 10% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 10% for Bermuda and 5% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas. The odds of Igor hitting land in the U.S. or Canada are probably close to their climatological 10% and 5% probabilities, respectively.

Elsewhere in the tropics
A new tropical wave (Invest 93L) emerged from the coast of Africa yesterday, and is already showing signs of organization. Most of the models predict 93L will develop into a tropical depression 2 - 4 days from now, and NHC is giving 93L a 30% chance of developing by Monday.

Next post
This may be my only post today; I'll have a new post Sunday morning.

Jeff Masters

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Quoting StormW:


In his video yesterday?

No, the video he post today, the Japanese model and I think he say the gfs.
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That what i been saying too Analyist. but some just believe that somehow this cent-atl trof is gonna lift or flatten out and igor will come West.and still waiting for this pattern change..
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469. IKE
ECMWF @ day 10....lower 48 has deflector shields up in 2010....and the clock is ticking....

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Quoting stormwatcherCI:
You preach about patience and sometimes you have less than anyone else. StormW, Dr Masters, Levi and you yourself said it will be a slow process. Dr Masters said "92L could wrap in some of the dry air to its northwest at times, slowing down development." Doesn't mean chances are less, does it ?
Ok? I'm not speaking about convective wane, I'm talking about the lack of a surface circulation.
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Quoting MiamiHurricanes09:
ASCAT revealed that a surface circulation is not present in the system. So, even though environmental conditions are conducive, it will take time for the mid-level circulation to translate towards the surface and close. We'll see what happens.


Considering its past of having a surface circulation, we know it has the capability. Within 48 hours this should be a TC. But I welcome a difference in opinion. Would be too boring without it lol
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Storms that form in gulf all going west toward mexico.
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Quoting CybrTeddy:
What your going to see happen is convection will continue to fade up until about 9 o'clock or so, and the 8 pm TWO will still have 60%, then there will be a popping of convection, that's the way these storms develop. 92L's been very similar to that of the invest that spawned Hurricane Dolly so far to me.
Agreed. +1
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Quoting StormW:


Some folks just never give it a rest, do they?

How you doin Analyst?


Good.

Getting real tired of the trolls though.

How about you, Storm?
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461. IKE
216 hours.....

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Quoting StormW:
Quoting Jedkins01:
I don't see why 92L will struggle with dry air. I have seen people look at water vapor satellite and see dry air on it and say that it could be a threat to a tropical system.

What people do not realize is water vapor satellite only shows upper level moisture. The lower half of the atmosphere, where most moisture is held in the tropics, does not show on water vapor satellite.

Therefore what may appear as dry air on satellite does not mean the air is overall dry. Water vapor satellite is not really designed for measuring moisture at all, rather it is used to get a better picture of what is going on in the upper levels as apposed to infrared or visible.

See almost all of moisture that a hurricane gathers does not come from the upper levels obviously, being that it is a tropical cyclone of course.

Therefore only PWATS give a great example whether dry air is actually a threat to a tropical system. Since this is the measurement for total atmospheric moisture.

Although dry air on water vapor satellite CAN indicate a very dry air mass, it certainly doesn't always. The upper levels can be dry, while the lower levels of the atmosphere can be very moist. There an atmosphere can also be very moist even if the the water vapor satellite shows dry air in the upper levels.


Dry air is a threat to a tropical cyclone IF the overall atmosphere is dry. Mainly the over low to mid level dry air.



That being said, overall the PWATS ahead of 92L look quite high in the Caribbean as they usually are, so I don't see why 92L has any dry air threat.

The air mass isn't as moist as it can be in the Caribbean, but there's plenty enough moisture to not threaten 92L.


I disagree with Dr. Masters in this case, because of my observation...

That's not really true...the milky colors are upper level...the orange and brown are mid level...that's why we can use water vapor imagery to show steering at the 500 mb level.



Yes but total atmospheric moisture can be quite high still even when water vapor satellite shows dry air.

Also, the air mass can be quite dry when the water vapor shows moisture.

For example, over Florida a few days back, the water vapor showed very dry air over the peninsula. But this was very deceiving, because the PWAT was still reading 2.17 inches due to very deep low level moisture, and sure enough, storms popped everywhere with daytime heating as usual. We even received 2.13 inches in 25 minutes from a very heavy storm, which is common this time of year in central Florida.


But still, my point being is water vapor satellite does not necessarily confirm whether or not a an atmosphere is over all moist or dry.



However you're right that my mistake about water vapor satellite only indicating upper level conditions is not true. It also does indicate what is going on in the mid-levels.
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Ike even the storm behind Igor is farther out to sea ,nothing is going to touch the east coast no matter what a NAO says,positive or negative.Not happening.Cape Verde season is one big fish.
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Quoting extreme236:


I don't see why it would be 30%. Your going to see convective fluctuations with a system like this. Environmental conditions nonetheless are rather conducive, especially as it moves out of the eastern Caribbean.
ASCAT revealed that a surface circulation is not present in the system. So, even though environmental conditions are conducive, it will take time for the mid-level circulation to translate towards the surface and close. We'll see what happens.
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Quoting TropicalAnalystwx13:
This should be classified already:



I don't get it. The thing just rolled off Africa...it needs a chance to prove its self in open water for a while. If it's truly a depression the NHC will classify it...I personally would like to see persistence for another 12 hours or so. We have all seen beautiful waves/lows fall off the African coast and turn into nothing. I think the NHC is doing the right thing and when it's time to classify, they will.
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What your going to see happen is convection will continue to fade up until about 9 o'clock or so, and the 8 pm TWO will still have 60%, then there will be a popping of convection, that's the way these storms develop. 92L's been very similar to that of the invest that spawned Hurricane Dolly so far to me.
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Quoting help4u:
All of these storms going out to sea looks like the pattern change all the models said would happen did not materialize.Big storms and big misses =quiet year for the states.Next week the pattern was suppose to change for 6 weeks now,looks like high major impact season will not happen.


We're not looking for Cape Verde systems to hit the US of A like a lot of you trolls think.

We're looking for home-grown storms in the Caribbean and Gulf to hit the US of A.
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450. IKE
Day 8 ECMWF.
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Stormw

That's not really true...the milky colors are upper level...the orange and brown are mid level...that's why we can use water vapor imagery to show steering at the 500 mb level.

The last models shown by Levi give you the reason in terms of a more westward pattern.
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All of these storms going out to sea looks like the pattern change all the models said would happen did not materialize.Big storms and big misses =quiet year for the states.Next week the pattern was suppose to change for 6 weeks now,looks like high major impact season will not happen.
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Igor has gotten a lot smaller today... we could see this ramp up fairly fast today
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Quoting MiamiHurricanes09:
There goes the convection. Considering it doesn't even have a surface circulation, I'd put the chances near 30%, rather than 60%.
Why so low?? It's got a good presentation on satellite. The NHC is just saying that there is a high possibility that in the next 2 days this thing could become a TD. Not in the next 12 hours. Plus, I thought it did have a 'well-defined circulation'. I guess it lost it.
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This should be classified already:

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Quoting winter123:


Historically a storm in Igor's position will likely miss the US. The pattern this year seems to support a recurve as well. I said "likely miss". Models aren't reliable that far anyway, even if the link you gave did go till where it threatens the coast.


Ike was suppose to go out to sea
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Igor continues to display a banding eye feature.
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Not too concerned with 93L. Should become Julia but I expect it to go out to sea.
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Quoting xcool:
92l better look Igor


92L definitely DOES NOT look better than Igor.
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Quoting hydrus:
Did you see the HWRF ?...Link


Historically a storm in Igor's position will likely miss the US. The pattern this year seems to support a recurve as well. I said "likely miss". Models aren't reliable that far anyway, even if the link you gave did go till where it threatens the coast.
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Quoting extreme236:


I don't see why it would be 30%. Your going to see convective fluctuations with a system like this. Environmental conditions nonetheless are rather conducive, especially as it moves out of the eastern Caribbean.
Quoting stormwatcherCI:
You preach about patience and sometimes you have less than anyone else. StormW, Dr Masters, Levi and you yourself said it will be a slow process. Dr Masters said "92L could wrap in some of the dry air to its northwest at times, slowing down development." Doesn't mean chances are less, does it ?


Agreed.
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Quoting AtHomeInTX:


Interesting. I'd never heard this before. Thanks. :)



No problem, weather is a very complex science! But I love it, it helps keep you humble, as long as you are willing to admit you are wrong, seems like the weather is always a step ahead of even the smartest of experts, and I'm not exactly the smartest of experts! lol

I'm just staring my MET degree towards FSU, it has me all the more pumped about weather!
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437. xcool
p
Member Since: September 26, 2009 Posts: 2 Comments: 15618
436. xcool
Member Since: September 26, 2009 Posts: 2 Comments: 15618
Quoting IKE:


Day 7...



Uhh.. thats not good... NOT GOOD, Good thing it's a model run :)

Looks like the EURO tries to go south of Bermuda, then recurving it.
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93L also lost some convection, but that isn't unexpected. I expect a TD possibly as early as tonight.
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433. IKE
ECMWF on 92L...keeps it at 1006 mb's til hitting the Yucatan and then gets it down to 1003 mb's in the Bay of Campeche...heading for Mexico.
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432. xcool
92l better look Igor
Member Since: September 26, 2009 Posts: 2 Comments: 15618
Quoting MiamiHurricanes09:
There goes the convection. Considering it doesn't even have a surface circulation, I'd put the chances near 30%, rather than 60%.
You preach about patience and sometimes you have less than anyone else. StormW, Dr Masters, Levi and you yourself said it will be a slow process. Dr Masters said "92L could wrap in some of the dry air to its northwest at times, slowing down development." Doesn't mean chances are less, does it ?
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Quoting MiamiHurricanes09:
There goes the convection. Considering it doesn't even have a surface circulation, I'd put the chances near 30%, rather than 60%.


I don't see why it would be 30%. Your going to see convective fluctuations with a system like this. Environmental conditions nonetheless are rather conducive, especially as it moves out of the eastern Caribbean.
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428. IKE
Quoting reedzone:


A category 4-5 heading for Bermuda.. Ouch!


Day 7...

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Quoting IKE:
Day 6 ECMWF...Link


A category 4-5 heading for Bermuda.. Ouch!
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Quoting jodi4lsu:



I guess that's why when we see "dry" air on these models in south Louisiana it is still muggy "gumbo" weather outside....interesting! i'm a believer!!!!



haha yes!


But even then, it can be deceiving that when the moisture is very high at ground level, PWATS can still be low!

Meteorology is a complicated science! If you try to simplify it too much, you'll get burned! lol


By the way, the only way to accurately measure total atmospheric moisture CONTENT is precipitable Water(or PWAT's for short).

Then you can be sure you have deep moisture, if the PWAT is 2.00 inches or higher, it is considered a moist tropical air mass. At least in Florida and the deep south that is.


However, in much of the country, 1.5 inch PWATS is considered deep moisture. Its all about relative to climate normals.
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Quoting IKE:
There goes the convection. Considering it doesn't even have a surface circulation, I'd put the chances near 30%, rather than 60%.
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424. IKE
Day 6 ECMWF...Link
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Quoting JupiterFL:


Thats because you are a much better person than the rest of us.


"rest of us", are to many people to argue against them, so is better I be quiet for now, I don't want to be see like I was talking in the name of other people I don't even know.:)
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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